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maandag 24 juli 2017

Paving the way for our presence on the Moon

Reading the books and watching the TV series “the Expanse” awoken my old boyish-dreams of our presence on the Moon. Growing up with a dad that introduced me to the fantastic worlds of Larry Niven, Brian Aldiss, Isaac Asimov, Jack Vance, and Arthur C. Clark, gave me hope for the future and it motivated me to start my studies in Space Engineering. The science fiction became real-life science and engineering and I began to understand why the future was not yet achieved. We have made space engineering very complicated and expensive, which allowed only nations to perform this type of activities. But, I am living in the future of my old heroes of words and spaceflight has a permanent role in our daily life.

And more and more young engineers want to participate, because space is not that complicated anymore. We evolve as humans, such that complicated problems in the past are simple issues in the future. James S. A. Corey (A.K.A. Daniel Abraham and Ty Franck) hints to this as well in the novels of "the Expanse”, where a 'simple’ mechanic makes nuclear fusion and complex astrodynamics calculations in the back of his mind. To make this reality, we need to educate our students with more ‘complicated’ techniques and tools than the guys from the Apollo program had at the time. In other words, if we want to go to the Moon again, we need to pave the way by educating our students in new and different theories and practises then we did before.

Artist's impression of project IRIS

And this is what I try to do in my role as lecture. Last month, ten of my students presented their Design Synthesis Exercise (DSE), this is their final project to complete the Bachelor of Aerospace Engineering at the TU Delft in the Netherlands. Staff members present an idea or problem for which students can prescribe and design a solution (some sort of aircraft or space vehicle). Thanks to "the Expanse” I was envisioning ways to bring humanity back to the Moon. A difficult problem, so how to do it? I thought of the French president de Gaulle, who decided to invest in the French highway infrastructure in a time of poverty (just after WWII), but ultimately this infrastructure boosted the French economy, tourisme, and mobility in ways that baffled de Gaulle’s critics.

The Moon needs infrastructure! Infrastructure that facilitates surface research platforms, mining missions and other human presence on the Moon. Not for the few missions and proposals that we have now, but for Moon missions and applications we have not yet thought of. So, during the DSE my students had to design an infrastructure system around the Moon that was capable of enabling 24/7 communication on the Moon surface (the complete Moon surface, so also the far-side and the poles). They had to design the constellation, the satellites themselves, a deployment strategy and the transfer trajectory. And they had to do it cheap! Some found my idea too complicated for 3rd year undergrads, but the students really showed several innovative ideas and were capable to construct a feasible design.

Logo of project IRIS

Their first innovative design is the transfer trajectory. Instead of using a simple Hohmann transfer, they opted for a low-energy ballistic transfer trajectory, in which the rocket flies to the Sun-Earth L2 equilibrium point and falls back to a Moon orbit, without the need for a large insertion thrust at Moon orbit (as you do in a Hohmann transfer). I provided the students with some basic on three-body problem mechanics, some literature, and a simple Matlab script that was able to propagate objects in space. The figure below shows the designed trajectory they came up with:

The complete low energy transfer trajectory in Sun-centred rotating frame designed by the students

This choice of transfer trajectory reduces the amount of propellant needed, extra mass you need to launch into space. Of course, this comes with a price. Instead of the 2-day travel time you have with a direct transfer, these type of trajectories could take several months. However, if you have the time (no humans onboard), why not? Furthermore, a ballistic transfer trajectory eliminates the need for a large complicated propulsion system onboard your spacecraft, because it does not need to slow down the spacecraft at the Moon orbit. This opens up a whole new type of satellites that could orbit the Moon.

Engineering drawings of one of the designed cubesat communication satellite, showing some of the internal and external subsystems. The satellite used a parabolic and a phased-array antenna for communication, hence the large solar cell array.

This relates to the second innovative idea of my students, which is to use multiple small but identical satellites that operated in a Swarm-type of constellation. Small satellites (like Cubesats) are making their way to professional applications here around Earth. Think about a company like Planet (Labs, used to) that uses cubesats to observe the entire Earth with their goal being to generate a real-time Google Earth. The don’t need a few big complicated satellites, they need a lot of cheap, small, and simple sats with a camera and a communication system to send the data back to Earth. Other applications are Earthquake warning system (QuakeSat), global Wifi (project Outernet), or understanding our atmosphere (QB50). Cheap to manufacture and launch (small is light) and the system’s reliability could be reduced, because if one sat fails multiple others are still present to fulfil the mission. And let’s just be honest, multiple satellite deployment is just so cool to watch:

This DSE project showed that students are capable of creating innovative ideas and are able to think about realistic solutions in space engineering. A new age of space engineering is at our doorsteps and it might open up interplanetary space for humanity.

Note: all figures were obtained from my students DSE report: Information Relay InfraStructure for translunar communication.